Fuel cell is a device for generating electricity by using hydrogen or methanol as fuel and oxygen or air as an oxidizer, and by using electron generated during an oxidation-reduction reaction.
Such a fuel cell has a configuration in which an anode and a cathode are formed at both sides of an electrolyte membrane made of a polymer. This configuration is referred to as a Membrane Electrode Assembly (MEA). Hydrogen or Methanol used as fuel is supplied to the anode and reacts upon electrode catalyst to generate hydrogen ion H+, while the hydrogen ion H+ passing through a polymer electrolyte membrane is coupled with oxygen in the cathode so as to generate pure water.
With fuel cell, forming the anode and cathode on the polymer electrolyte membrane can be classified into two methods.
First, electrodes can be formed on a gas diffusion layer by coating catalyst ink on the gas diffusion layer, i.e. a carbon paper or carbon cloth with porosity. Next, a membrane-electrode assembly is manufactured by heating and pressing the electrolyte membrane and the gas diffusion layer coated on electrodes. The membrane-electrode assembly manufactured by such a method lacks contact of the electrolyte membrane to the catalyst layer, thereby causing the increasing of interfacial resistance.
Second, catalyst ink is coated on the surface of a membrane so as to form electrodes on an electrolyte membrane. In this method, the ionic contact of the electrolyte membrane and the catalyst layer is secured in comparison with the first method, so as to improve the capability of the fuel cell. However, this method makes it difficult to manufacture the fuel cell. Various kinds of methods such as spraying, painting, patch coating and screen printing have been developed in order to coat the catalyst ink on the surface of the membrane. However, these methods make the speed of manufacturing fuel cell slow. During the manufacturing of fuel cell, a great amount of solvent in the catalyst ink may cause the membrane to swell, thereby changing the size of the membrane. Thus, it may be difficult to manufacture preferable electrode.
On the other hand, one or more protecting film layers may be added on the catalyst coated membrane in order to handle the product more conveniently and prevent injury to the membrane. Since the exposed region of the polymer electrolyte membrane on which the catalyst is not coated in the catalyst-coated membrane may absorb moisture in the atmosphere and expand, it is difficult to assemble a stack when the membrane-electrode assembly using the catalyst-coated membrane is applied to a stack. Therefore, a protecting film layer is coated on the exposed region of the membrane to increase the mechanical stability of the membrane-electrode assembly made by the catalyst-coated membrane, thereby preventing injury to the membrane and facilitating the stack assembly.
According to the conventional art, separate processes are required to solve the above-mentioned problem. Specifically, the catalyst layer is formed on both surfaces of the polymer electrolyte membrane. Then, the protecting film is coupled to the exposed region of the membrane by heating and pressing the protecting film, or attached to the membrane by an adhesive. However, since the conventional art requires a number of processes such as a catalyst coating process and a protecting film coating process, etc, there is a problem in that it takes much time to perform the processes.